This inventor's U.S. Pat. No. 3,903,227, dated Sept. 2, 1975, shows a vulcanization system of this nature wherein a tire is placed within a pair of dies, the dies are closed, a tightly closed space thus being formed including the interior of the tire, the space is directly supplied with a pressure medium, and the medium is heated by means provided in the space.
During such vulcanization, a problem arises at an initial stage in the process, because a green tire is placed within the dies soon after a previous vulcanized tire is removed from the dies. The problem may be described as follows.
At the time when a green tire is placed within the widely opened dies, the tire itself is also spread open and the beads are spaced far apart; also the tire is relatively stiff at the ambient (low) temperature. The dies which were heated by the previous vulcanization cycle are then closed on the tire while they are hot. Immediately after the dies start to close, the bead seats of the dies engage the tire beads, thereby compressing the beads axially toward each other against the rigidity of the tire, and the tire tread is expanded outwardly. During the closing movement of the dies until the tread compressively engages the interior die surfaces, the tire bead surfaces rub with a considerable pressure against the hot bead seats of the dies. This heated rubbing and pressure may cause local release and/or failure of the surface rubber layer forming the tire beads.
Another problem is that it takes a relatively long time to complete the vulcanization of a tire when it is placed at the ambient temperature within the dies and then heated to a predetermined temperature, because the tire consists of a rubber material which has poor heat transfer characteristics.
It is a general object of this invention to provide a novel method of preheating and preforming a green tire to facilitate the subsequent vulcanization of the tire.